The central focus of the proposed research program is to develop a clear understanding of the membrane mechanisms in excitable tissues and how these mechanisms regulate the activity of the cells involved. The studies will be concerned with passive ion permeability in axons and muscle; active transport of ions in axons and muscle; membrane control of metabolism in muscle, excitation-contraction coupling and neuromuscular transmission. Measurements will be made of various electrical, ionic, optical, metabolic, energetic, and where appropriate, mechanical properties of excitable cells. Attempts will be made to relate these to morphological features of the membranes and cells as revealed by electron and light microscopy and to define the physical and chemical factors involved in these properties. BIBLIOGRAPHIC REFERENCES: Bezanilla, F. and P. Horowicz, 1975. Fluorescence intensity changes associated with contractile activation in frog muscle strained with Nile Blue A. J. Physiol., 246:709-735. Dulhunty, A. and P. Horowicz, 1975. Frog muscle membrane potentials in low external K solutions. Fed. Proc., 34:467.